1. Field of the Invention
This invention relates to moulding machines and has been devised particularly but not solely to provide moulding machines for the manufacture of articles from fibrous suspensions, such as suspensions of cellulose or synthetic polymer fibres or mixtures of such fibres, and especially from lignocellulose fibres such as are used in papermaking, and the fibre recovered from recycled waste paper.
The invention may also be used in the manufacture of moulded articles generally, wherein the moulded articles are formed upon, and take their shape from a die or a set of dies, using materials such as fibrous suspensions and thermoplastic sheet.
The invention and prior art is described by way of example, using the manufacture of articles by moulding from fibrous suspensions, but the invention may also be employed to advantage in manufacture by thermoforming from thermoplastic polymer sheet.
2. Description of the Related Art
In background articles may be moulded from fibrous suspensions, the fibre or fibrous mixture suspended in a fluid, to be deposited on the surface of a porous mould or die, the fluid passing through the pores, leaving the fibres behind to form the desired shape on the working surface of the mould or die.
The fluid commonly used to suspend the fibre is water, in a so-called wet forming process, with the suspension loosely referred to as pulp. Steam and/or air and/or other gases may also be used as the fluid, in which case the process is described in the art as a dry or semi-dry forming process. An advantage of water is that it has the ability to suspend the fibre reliably in the form of a pulp feedstock during preparation and storage, and delivery to the moulding machine, enabling the convenient inclusion of various additives both to advantageously modify the moulding process on the moulding machine and also the properties of the moulded article to suit various end uses. When the fibre is or contains lignocellulosic fibre such as papermaking fibre which may be recovered from waste paper for example, another advantage of water is that it enables hydrogen bonds to be developed between the fibres, either as the only bond or in association with other adhesives so connecting the fibres together at junctions in the completed article, hydrogen bonds being the principle bonding means used by papermakers.
In a dry forming process, additional adhesive is invariably required unless the article is held under pressure at a temperature high enough to fuse the natural polymers (principally the lignin) in the formed mass, because significant hydrogen bonding is not developed in a dry forming process.
While water is the most common medium used to transport fibres for moulding it also has some disadvantages and the main disadvantage of water is that when the fibres have been deposited on the mould or die surface, substantial energy is required to remove the water again to produce a usefully rigid article.
The source of lignocellulose fibre most commonly used is recycled waste paper although virgin fibre or a fibre mixture may also be used, including various polymer fibres which of course do not develop hydrogen bonds. When present in large proportions or as the sole fibre, polymer fibres may be bonded by fusing with heat.
After removal of sufficient water by draining, pressing, and the like, to enable the moulded article to be further processed it is transferred directly or by means of a co-acting transfer die or dies of a shape generally matching the moulding die, to a drying facility, where further water is removed using heat. In a dry forming process the dies may be heated to cure a bonding agent. A drying facility may be used, which is typically an oven, including a conveyor onto which the moulded article is deposited, to be conveyed through the oven, to emerge as the dried or cured rigid article of a substantially predetermined moisture content.
In practice, although the moulding process can be accomplished with a single moulding die with or without a single transfer die, the moulding machine more usually includes a plurality of moulding dies and a plurality of transfer dies to effect moulding and transfer of the articles more or less continuously at a satisfactory production rate. Sometimes a lesser number of transfer dies than moulding dies is used, each transfer die serving more than one moulding die, but nevertheless with generally matching shapes and the dies co-acting in sets. The plurality of moulding dies are arranged to move on a path which includes immersing them into a vat of the suspended pulp feedstock to collect or form the moulded article on the porous moulding surface of the die, and the plurality of transfer dies (where used) are also arranged to move on a separate path which includes engaging in co-acting sets with the moulding dies to effect transfer of the moulded articles prior to drying them, or in the case of a dry forming process, to press the article and apply heat to cure a bonding agent.
During engagement of co-acting sets any separate paths must be parallel for a time, and the die sets must be moving at similar speeds to remain properly engaged and this necessity places significant limitations on prior art moulding machines of the continuous-path type, especially where the article requires moulding of deep cavities.
Separate pressing dies may be used either to improve the shape or finish of the article or to provide conditions to bond the moulded material together. When the pressing process is performed on the moulding line the separate pressing dies also have to be coordinated with the other functions of the moulding machine.
The simplest form of a moulding machine arrangement is a reciprocating system with the moulding die or dies reversing repeatedly on a path to accomplish the process. This form of moulding machine is relatively simple to control as the path is usually linear and there are end positions at each end of the path. The reciprocating moulding machine solution is usually applied to comparatively low volume production, often for deep cavity mouldings, and has an advantage of simplicity and low capital cost for such purposes.
For large scale production the common prior art solution is to provide continuous-paths for the dies to follow by mounting them on a rotating framework or rotor, for example a moulding die rotor and a transfer die rotor, which are permanently mechanically interconnected so as to keep them in the correct relative positions throughout the sequences, the rotors usually moving continuously at a constant speed during the production process. The essential sequences of operations required for moulding machines with continuous-path mounted dies become much more difficult to provide and control and the prior art versions of these machines are not suited to deep cavity mouldings, mainly because of interference between moulding and transfer dies as they enter and leave cavities while moving on a non-linear path. Irrespective of whether or not transfer dies are used, the wet articles may also be required to be deposited accurately on a conveyor passing through a drying oven, especially where dryer trays are used. This requires yet further co-ordination. Often a subsidiary function of the transfer dies is pressing to achieve mechanical compaction and accuracy of shape of the article and removal of some water by squeezing prior to a further drying stage, or application of heat in a dry forming process.
Associated with the need for correct register of the moulding and transfer dies are functions such as the application of alternating vacuum and pressure to the moulding dies at the appropriate time to draw fluid through holes provided in order to form the pulp feedstock on the porous working face and effect transfer of the moulded article respectively, and application of alternating vacuum and pressure pulses to the transfer dies (which are also provided with holes), at the appropriate times to effect transfer of the moulded article, and release of the article for placement for drying or stacking. In addition, water sprays and air showers are often provided in order to clean the dies, to assist in transfer or positioning of the article at various stages of the process and to xe2x80x9cwashxe2x80x9d the product to improve its surface finish and edge definition. The functions must all take place at the correct stage in a predetermined sequence to accomplish reliable and continuous manufacture of the article.
Various solutions are provided in the prior art to accomplish the sequences and some examples of embodiments of the common moulding machines used are disclosed in New Zealand patents, 113979 121548, and 140909 by Keyes Fibre Company who have operated such machines in the past through their licensees in New Zealand, and in other countries. Moulding machines of these general designs are widely used in the pulp moulding industry worldwide and have been generally unchanged for many years.
Relative movement together and accurate positioning of moulding dies and transfer dies is accomplished in the prior art by the use of mechanical cams which track the transfer dies along a common or parallel path and at the same speed as the moulding dies for a sufficient path length to effect transfer of the article, and because relatively large mechanical forces are involved, the cam tracks and cam followers and all the associated components, have to be of very robust and heavy construction. They not only become expensive but once configured are very difficult and time consuming to change, except perhaps by modification or replacement during a major machine re-fit. Secondary cams and/or levers are also provided to operate valves for application of vacuum, water, and pressure to components at the correct stage of the sequence. The cams and the configuration of the paths followed by the components on the moulding machine also predetermine the range of cavity depth that can be moulded on a particular machine. Once set up, the functions are generally insensitive to operating variables such as pulp consistency, temperature, and changes in the waste paper feedstock for example, and all of these things can directly affect the quality and utility of the finished article as well as the production speed. When a plurality of moulding dies are fitted to such a machine they must all be very similarly matched since the process is a compromise which does not allow several different articles with different moulding characteristics to be produced in the same production run.
When the moulding machine is in production it requires constant monitoring and attention by operators who are able to make only limited on-the-run adjustments, due to the rigid mechanical interconnections of the machine design. Changes are made to the pulp consistency and machine speed and various pressures in order to produce articles within the predetermined product specifications and quality, and these require the attention and decisions of a skilled operator. A breakdown can typically involve loss of a mechanical connection and loss of co-ordination between the components and functions, and often serious mechanical damage to the moulding machine, including the dies should they come together in the wrong way.
With moulding machines of a continuous-path type particularly, it not only becomes difficult to provide the solutions to co-ordination of the various functions but it becomes very difficult or impossible to tune or adjust the various coordinated and sequenced functions on-the-run in order to maximise production and article quality. Even the behaviour of the individual dies in a set can be different due to slight variations in them and their position on the machine and in the prior art adjustments for differences at this level become a complex and time consuming job for a skilled technician. Operators must always be present to make compromises based on their skill and experience, and make the limited adjustments possible to machine speed, pulp consistency, vacuums, pressures, and the like in order to maintain satisfactory manufacture.
Thus, it is an object of this invention to provide continuous-path moulding machines which overcome or minimise at least some of the forgoing disadvantages in a simple and cost effective manner.
It is a further object of this invention to provide continuous-path moulding machines with predetermined self-correcting operating capabilities, capable of operating for extended periods without operator intervention and capable of remote monitoring and control.
It is a further object of this invention to provide continuous-path moulding machines with greater versatility and reliability than prior art moulding machines or to at least provide the public with a useful choice.
Accordingly, in one broad form of the invention, there is provided a continuous-path moulding machine (as defined herein) for manufacture of moulded articles, including at least one moulding or forming die moving continuously or stepwise forward on a primary path and at least one transfer or pressing die moving continuously or stepwise forward on a secondary path, and wherein at least one said path is a continuous-path loop, the arrangement being such that a component on said continuous-path loop passes a given fixed point on said continuous-path loop repeatedly, and wherein a plurality of discrete reference positions are provided on at least said primary path, and wherein said discrete reference positions generate at least one position defining signal on said primary path, and wherein said at least one position defining signal is transmitted to at least one DIOC (as defined herein), and wherein said DIOC includes associated customised software containing xe2x80x9cif-thenxe2x80x9d type instructions (as defined herein), and wherein at least one communication system is provided to enable signals to be communicated from a stationary component of said continuous-path moulding machine to at least one component on a path of said continuous-path moulding machine to maintain real time relationship and positional control between said at least one moulding or forming die on a primary path and said at least one transfer or pressing die on a secondary path while said continuous-path moulding machine is operating to produce moulded articles.
Preferably said primary path is a continuous-path loop.
Preferably said secondary path is a continuous-path loop.
Preferably a plurality of discrete reference positions are provided on said secondary path, and wherein said discrete reference positions generate at least one position defining signal, and where said at least one position defining signal is transmitted to at least one DIOC, and wherein said at least one DIOC includes associated customised software containing xe2x80x9cif-thenxe2x80x9d type instructions.
Preferably said at least one DIOC receives at least one position defining signal transmitted from a primary path of said continuous-path moulding machine and at least one position defining signal transmitted from a secondary path of said continuous-path moulding machine.
Preferably said communication system is selected from a slip-ring system, a rail and conducting brush or shoe system, a slip-disk and conducting brush system, an infra-red or visible spectra light beam system, or a radio frequency signal system.
Preferably said communication system is a slip-ring or slip-disk system.
Preferably said discrete reference positions are identified one from another reference position.
Preferably said discrete reference positions are identified one from another reference position by counting each reference position from a datum or base reference position.
Preferably said discrete reference positions are positively identified one from another reference position by each being provided with a unique code.
Preferably said code is characterised by a signal frequency or intensity.
Preferably said code is characterised as a digital code.
Preferably said digital code is selected from a simple binary code, a binary code decimal, or a variation of a binary code decimal known in the art as Gray Code.
Preferably said discrete reference positions are provided by one or more rotary encoding devices.
Preferably one or more rotary encoding devices are directly mechanically connected to a shaft having a reliable and accurate rotational relationship to the movement of a primary or secondary path of said continuous-path moulding machine.
Preferably one or more rotary encoding devices are directly mechanically connected to a mainshaft having a 1 to 1 relationship to a primary or secondary path of said continuous-path moulding machine.
Preferably one or more rotary encoding devices are driven faster than the continuous path to which they relate so as to multiply the number of codes or pulses for each revolution of said one or more rotary encoding devices to enhance the number and resolution of discrete reference positions on a continuous path loop of said continuous-path moulding machine.
Preferably a primary path and a secondary path are provided with a conventional mechanical connection therebetween to establish and maintain a positive positional relationship between said primary path and said secondary path of said continuous-path moulding machine.
Preferably said continuous-path moulding machine includes at least one primary continuous-path loop and at least one secondary continuous-path loop, wherein discrete reference positions are provided by at least one encoding device associated with each of a primary continuous-path loop and a secondary continuous-path loop to generate a plurality of position defining signals from said at least one encoding device associated with each continuous-path loop and wherein said position defining signals are input to and sampled at substantially predetermined intervals by at least one common DIOC, said common DIOC including customised software containing xe2x80x9cif-thenxe2x80x9d type instructions, and wherein positional errors between a primary continuous-path loop and a secondary continuous-path loop are determined by comparisons between actual positions as indicated by said position defining signals and target positions as defined in said customised software, said positional errors initiating a response of output correction signals at a substantially predetermined interval frequency to closed servo loop operating system including servo amplifiers driving associated servo motors on both a primary continuous-path loop and a secondary continuous-path loop to maintain real time relationship and positional control between a primary continuous-path loop and a secondary continuous-path loop of said continuous-path moulding machine while said continuous-path moulding machine is operating to produce articles.
Preferably said substantially predetermined interval frequency is between 50 and 2500 times per second.
Preferably said substantially predetermined interval frequency is between 1000 and 2000 times per second.
Preferably said DIOC includes one or more common personal computers fitted with at least one data acquisition and control input/output card.
Preferably said DIOC includes one or more programmable logic controllers, commonly known in the art as a PLC.
Preferably said DIOC includes an interface with at least one other personal computer to enable monitoring of said continuous-path moulding machine while said continuous-path moulding machine is operating to produce articles.
Preferably said at least one personal computer is adapted to enable changes to be made to said associated customised software containing xe2x80x9cif-thenxe2x80x9d type instructions while said continuous-path moulding machine is operating to produce articles.
Preferably said interface includes a modem for transmission of data between said at least one DIOC and said at least one personal computer.
Preferably said at least one personal computer is located at a distant site, remote from said continuous-path moulding machine.
Preferably transmission of data between said at least one DIOC and said at least one personal computer includes a telephone link.
Preferably transmission of data between said at least one DIOC and said at least one personal computer includes a radio link.
Preferably at least one moulding or forming die moves stepwise forward on a primary path.
Preferably at least one transfer or pressing die moves stepwise forward on a secondary path.